The present inventive concept relates to image sensors and methods of manufacturing same. More particularly, the inventive concept relates to backside-illuminated image sensors and related methods of manufacture.
In common conventional methods of manufacture for image sensors (e.g., CMOS image sensors), transistors are formed on a semiconductor substrate on which photodiodes have been formed for each image sensor pixel. Multi-layered metal interconnects and interlayer dielectrics are then formed on the transistors. Finally, color filters and micro-lenses are formed on the interlayer dielectric.
Image sensors having a structure consistent with this conventional manufacturing approach require light focused by a micro-lens to pass through a number of different interlayer dielectric layers before reaching a photodiode. This optical pathway tends to incorporate a great deal of reflection and suffers from optical shielding as a result of the multi-layered metal interconnects. As a result, light collection ratio at the photodiode is relatively low, and image quality suffers.
Such problems are mitigated to a certain degree in so-called backside-illuminated image sensors. Backside-illuminated image sensors provide an optical pathway for photodiode-incident light through the back-side of a constituent substrate, wherein the opposing front-side of the substrate is conventionally used to accommodate the afore-mentioned metal interconnects and interlayer dielectrics. Unfortunately, conventional backside-illuminated image sensors suffer from significant crosstalk between proximate pixels due to light diffraction. Such crosstalk tends to increase as the wavelength of incident light becomes longer and the integration density of image sensor increases.